The present invention relates to a zoom lens and zoom lens barrel and more particularly, it relates to a zoom lens and zoom lens barrel that have an improved feature of follower pins for the zoom lens configured correlative to resin barrel with cam mechanism.
A zoom lens barrel is, in general, of a tiered configuration that includes mutually telescopic barrel components of an adjusting ring rotatably manipulated for zooming by a user, a cam barrel provided with cam grooves and capable of rotating, a linearly moving barrel provided with grooves for linear movement and unable to rotate in itself, and n frames holding n groups of lenses (n is an integer), which are arranged in such an order from the outermost to the innermost. The n-th frame holding the n-th group of lens, for example, is fixedly fitted on a cam follower pin, which is, in turn, fitted in the groove for linear movement and the cam groove. Rotation of the adjusting ring is transmitted to coupling members so as to circumferentially rotate the cam barrel
As the adjusting ring is rotated to cause rotation of the cam barrel, the cam follower pin moves in a segment where the cam groove is registered with the groove for linear movement, which brings about desired movement of the n-th group of lenses along on the optical axis.
As to the above-mentioned zoom lens barrel, fabricating the cam barrel of metal results in considerable increase in a manufacturing cost. Specifically, it is necessary that the cam barrel has associated lens frames stably move along in its respectively corresponding cam grooves so as to retain optical performance of the zoom lens, and therefore, the cam grooves must satisfy a dimensional precision within a tolerance of 0.01 mm. Die casting alone results in products of unsatisfied precision inferior to the above-identified tolerance level, and refinement of the fabrication process in combination with a precision grinding procedure is required although this causes significant increase in the manufacturing cost.
If the cam barrel for the zoom lens is made of some type of plastic by metal-die injection molding to define the cam grooves therein with a high dimensional precision, the cam grooves must be shaped in cross sections widening toward the outer circumference to release the die from molded plastic. In such a situation, the cam follower pins must be correspondingly molded in shapes spreading toward the heads, and moreover, elastic elements such as spring have to be used to make elastic contact of sliding surfaces of the cam follower pins with the cam grooves, so that the cam follower pins can be assuredly fitted in the cam grooves and be smoothly slid therein. This design yields adverse effects of increase in the number of components including the elastic element such as the spring and associated elements and increase in the number of process steps in assembling the components, and besides, the additional components such as the spring associated with the cam follower pins resultantly are the cause of increase in dimensions.
The present invention is intended to overcome the above-mentioned disadvantages of the prior art zoom lens barrel, and it is an object of the present invention to provide a zoom lens and zoom lens barrel superior in precision and excellent in manipulability, having a feature of combination of plastic cam barrel that retains a high dimensional precision and brings about decrease in a manufacturing cost, with the reduced number of components associated with cam follower pins.
In accordance with the present invention, a zoom lens is comprised of a plurality of groups of lenses, an adjusting ring rotated for zooming by a user, a cam barrel provided with cam grooves and capable of rotating due to turns of the adjusting ring, a linearly moving barrel provided with grooves for linear movement and unable to rotate, n frames for holding n of the groups of lenses (n being an integer greater than 1), and cam follower pins fitted in the cam grooves and the grooves for linear movement and fixed to the first to the n-th frames for correspondingly holding the first to the n-th groups of lenses, respectively, in which the cam barrel is molded of plastic and has the cam grooves defined in cross-sectional shapes widening toward the outer circumference, and the cam follower pins are elastically transformed so as to be fitted in the cam grooves.
In another aspect of the present invention, a zoom lens barrel is comprised of an adjusting ring rotated for zooming by a user, a cam barrel provided with cam grooves and capable of rotating due to turns of the adjusting ring, a linearly moving barrel provided with grooves for linear movement and unable to rotate, a lens frames holding lenses, and cam follower pins fitted in the cam grooves and the grooves for linear movement and fixed to the lens frames, in which the cam barrel is molded of plastic and has the cam grooves defined in cross-sectional shapes widening toward the outer circumference, and the cam follower pins are elastically transformed so as to be fitted in the cam grooves.
In this aspect, the cam follower pins have their respective cam groove engagement sections formed in cup-like shapes spreading toward the tops.